The present invention relates to a ribbon cartridge construction and a method of assembling same. In particular the present invention is directed to the shielding of an exposed run of ribbon at the ribbon access window of a ribbon cartridge housing.
Currently, many typewriters, printers and other business machines include printing mechanisms which utilize a ribbon cartridge for the supply of ribbon which has a housing forming a ribbon access window at the outer perimeter thereof for exposing a run of ribbon for printing on an oppositely facing surface. The printing mechanism strikes the exposed run of ribbon from behind at a predetermined portion thereof to effect printing on a oppositely facing surface such as a piece of paper.
Since the requirements for these types of printers is that, in addition to good print quality, they print at high speed, it is necessary that the exposed run of ribbon be extremely close to the printing surface and that the printing mechanism also be close to the exposed run of ribbon so that the total path of travel of a printing element striking the ribbon and, thereafter the printing surface, is small.
It has been found that when the inked surface of the ribbon is disposed close to the printing surface, the relative movement of the printing surface and the ribbon causes smudging and smearing of the ribbon ink on the printing surface. Since this effect is highly undesirable, the art has developed the use of a shield with a printing aperture having the area of the predetermined portion of the exposed ribbon to protect the printing surface from the remaining exposed run of ribbon.
Commercially available shielding has taken many forms. For example, one type of shield is inserted at the ribbon access window through the ribbon inlet and outlet apertures prior to the mounting of the cover on the top of the cartridge. This shield is dropped in from the top and permanently mounted in place by the covering of the cartridge. In an alternative method, the shield is fixed in place on the outside of the cartridge by double sided tape.
The former method of shielding has the disadvantage that it can only be performed by the cartridge manufacturer and the shield cannot be removed or replaced by the user. The latter method has the disadvantage that it is difficult to properly align the shield aperture to the predetermined portion of the exposed ribbon which is struck by the printing mechanism. Moreover, the use of adhesive to fix a shield on the cartridge perimeter is not reliable.